The only company I know of making airshocks right now is Tenneco and maybe some Arvin inventory still floating around. Neither one is what I'd consider a quality shock. KYB's are decent, have you checked to see if they have something?
Airsprings (helper bags) would work much better and last longer, check out
Air Lift for those.
Not all shocks can be mounted upside down, namely twin tube gas-charged type. Monotubes can be mounted upside down, twin-tube non-gas (hydraulic) don't work any way you mount them...